1. Field of Invention
The present invention relates to tools used in the manufacture of thin films. In particular, the present invention relates to a device for dispensing a uniform thickness of an initially viscous liquid material onto a planar work surface in order to produce a film of predetermined thickness, length and width. This thin film of viscous liquid material is then further processed to create a solid film of adhesive material.
2. Description of the Prior Art
Methods have been employed to spread and distribute materials such that a layer of uniform thickness of that material may be spread on a surface. "Doctoring blades" are generally known to accomplish this function. The material is typically placed onto an application surface, and a doctoring blade is passed over the material to spread it into a layer or film of uniform thickness. The doctoring blade consists of a bar or spreader mounted on wheels that support the bar above the application surface. The bar may be adjustably mounted on the wheels so that the elevation of the bar above the work surface may be varied. As the doctoring blade is rolled across the material on the application surface, the bar spreads the material into a layer of uniform thickness.
A problem with prior doctoring blades is that while they are suitable for defining the thickness of distribution for some types of materials, they are not readily suitable for creating a thin uniform film of an adhesive viscous liquid. When spreading an adhesive viscous liquid onto an application surface, the spreader and the wheels of the doctoring blade become coated and clogged with the adhesive and require cleaning. Cleaning and maintenance of such prior apparatus can cause undesirable downtime in the production of adhesive thin films.
When the spreader of the doctoring blade becomes coated with the adhesive, the coating can affect the relative height of the spreader in relation to the wheels of the doctoring blade. This can produce a film of adhesive that is not of the desired thickness. Also, when the adhesive has collected on the spreader unevenly, it can undesirably affect the uniformity of the thickness of distribution of the adhesive viscous liquid.
When the wheels of the doctoring blade become clogged (e.g., by the adhesive), it restricts the smooth travel of the doctoring blade across the application surface, affecting the uniformity of the distribution of the adhesive viscous liquid. Additionally, when the wheels of the doctoring blade have been coated, it also affects the relative height of the spreader in relation to the application surface, undesirably increasing the thickness of the film of adhesive viscous liquid.
It is also known that with some doctoring blades, the option exists to increase the distance between the wheels of the doctoring blade. This however also causes an undesirable non-uniform distribution of the adhesive viscous liquid because as the wheels are moved further apart, the spreader may sag in the middle. This undesirably causes the sides of the distributed film to be of greater thickness than the center of the film of adhesive viscous liquid.
Screeds are also generally known. Typically a screed consists of a leveling bar which is passed over a wet concrete form to level the concrete. The form consists of horizontal bars which contain the wet concrete (as for the sides of a sidewalk) defining not only the width of the concrete, but also the maximum height of the concrete. As a screed is passed over the form, the concrete is distributed evenly within the form's boundaries, and excess concrete is removed by the screed such that the plane formed between the top edges of the form defines the height of the concrete. Also known is a paving device using a screed wherein the paving material is supplied through a gravity fed hopper. This is the subject of U.S. Pat. No. 5,615,973 to Campbell.
Such prior screeds are not suitable for spreading films of adhesive viscous liquids. The manufacture of forms of varying lengths and thinness is not suitable for the production of a film of adhesive viscous liquid, which is typically very thin. Additionally, the adhesive viscous liquid can coat the surfaces of the form and leveling bar, creating an undesirable lack of uniformity in the thickness and width of the film of adhesive viscous liquid.
Another problem with both doctoring blades and screeds is that it is difficult to accurately measure the precise amount of material needed to create a layer or film of predetermined length. With a doctoring blade, an approximate amount of material is spread on the application surface and is then distributed on the surface by passing the doctoring blade over the material. When applying a film of adhesive viscous liquid with a doctoring blade, the excess adhesive not only coats and clogs the surfaces of the doctoring blade but also may go to waste.
With a screed such as one incorporated in a paving apparatus, an approximate amount of paving material is placed within the form, and the excess material is removed. Screeds of this configuration, when used to create a thin film of adhesive viscous liquid not only become coated with excess adhesive, but may also allow the excess to go to waste.
Another problem is that both screeds and doctoring blades require a separate means to convey and dispense the material to be distributed. The requirement of conveyance and dispensing means makes screeds and doctoring blades operable only in conjunction with large, supplemental equipment. Screeds used in the creation of level pavement or roads are used in conjunction with cement trucks, large hoppers, and conveyors which are hydraulically, pneumatically or electrically operated. Doctoring blades typically distribute materials fed through them by conveyor belts. These screeds and doctoring blades thus are not suitable for manual or hand-held operation because of the requirement for separate conveyance means.